AD5791: Bad results for linearity measurement

Hi,

I am using a precision dac source circuit based on the AD5791 20 bit DAC. The problem faced by me is, while 1 LSB - max INL/DNL spec is guaranteed for the DAC including the recommended AD8676BRZ voltage reference buffers and AD8675ARZ output buffer, the linearity results obtained by me during measurement using agilent 3458A digital multimeter are very bad. To reduce test time, i had used a step size of 32, and done a measurement run across the full range, ie -10 to +10V, but the INL results obtained are exceeding 3 LSB, and this LSB is at 15 bit level, not 20 bit. So if we calculate at 20 bit level, results are much worse.

My DAC source uses a supply of +/- 14V, and uses the recommended AD8676BRZ voltage reference buffers and AD8675ARZ output buffer, and the buffered output is applied to an inverting adder using OPA1612 opamp, which is meant to add dc offset to the DAC output. The test was done at 0V DC offset. In the test, sufficient settling time has been given for the DAC output to settle( about 0.1ms). The INL plot acquired looks strange as well. Please find the following attachments

Attachments:

1.The schematic of the entire circuit: Page nos 6 and 8 depict the connections associated with the DAC part. Also the test was conducted with R75=50E( page no 8)

2.The INL-DNL plots obtained with stepsize of 32, and calculated with 15bit resolution LSB, (ie LSB=20/(2^15))

Thanks

Anoop

attachments.zip
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  • Hi Estibaliz,

    Thanks a lot for your prompt response. Could you give us a brief estimate of how much the performance of the DAC will be affected by using ADR01 reference, that is, an approximate idea of the max/min INL-DNL figures we can hope to achieve using ADR01, since we are into an advanced stage of the project, and it wont be too feasible for us to change to LTZ1000 at the moment. If we can get a rough idea of the baseline performance with ADR01 reference, we can set the specifications for the project likewise.

    Also, could you offer us a logical explanation for the particular shape of the INL curve attached to the previous mail? It seems to increase steadily till some voltage, then decreases, and when reverses with opposite polarity. Is this pattern of INL expected?

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  • Hi Estibaliz,

    Thanks a lot for your prompt response. Could you give us a brief estimate of how much the performance of the DAC will be affected by using ADR01 reference, that is, an approximate idea of the max/min INL-DNL figures we can hope to achieve using ADR01, since we are into an advanced stage of the project, and it wont be too feasible for us to change to LTZ1000 at the moment. If we can get a rough idea of the baseline performance with ADR01 reference, we can set the specifications for the project likewise.

    Also, could you offer us a logical explanation for the particular shape of the INL curve attached to the previous mail? It seems to increase steadily till some voltage, then decreases, and when reverses with opposite polarity. Is this pattern of INL expected?

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